Generally speaking, a semi-trailer truck, more commonly called a semi-truck, is the combination of a tractor unit and one or more semi-trailers to carry freight. It is also variously known in the United States as a semi, tractor-trailer, big rig, or eighteen-wheeler. A semi-trailer attaches to the tractor with a fifth wheel hitch, with much of its weight borne by the tractor. The result is that both tractor and semi-trailer will have a distinctly different design than a rigid truck and trailer.
The most common tractor-cab layout has a forward engine, one steering axle, and two drive axles. Ubiquitous in Europe, but less common in North America since the 1990s, is the cabover engine configuration, where the driver sits next to, or over the engine. With changes in the US to the maximum length of the combined vehicle, the cabover was largely phased out of North American over-the-road (long-haul) service by 2007. Cabovers were difficult to service, as the cab could not be lifted on its hinges to a full 90-degree forward tilt, severely limiting access to the front part of the engine. As such, the instant disclosure may be directed to a standard tractor with a conventional cab with a forward engine under a hood.
The cabin or cab of a truck is an enclosed space in a truck where the driver is seated. Modern long-haul truck cabs usually feature air conditioning, heater, a sound system, and ergonomic seats for driver and passenger comfort. A sleeper, also known as a sleeper berth or bunk, is a compartment attached to the back of the cab where the driver can rest while not driving, sometimes seen in semi-trailer trucks. Sleepers can range from a simple small bunk to a large sleeping area. Conventional cabs are the most common in North America, where the driver is seated behind the engine, as in most passenger cars or pickup trucks. Conventional cabs are further divided into large car and aerodynamic designs. A “large car” or “long nose” is a conventional truck with a long hood. With their very square shapes, these trucks experience a lot of wind resistance and typically consume more fuel. By contrast, aerodynamic cabs are very streamlined, with a sloped hood and other features to lower drag. The front doors are behind the front tires. Access to a conventional cabin is commonly by steps at or near the fuel tanks behind the front tires.
Truck cabs are ridged structures that need to be isolated from the chassis upon which they are mounted. This is done via a cab suspension system. Frames undergo bending and torsional movements due to the loads they carry, uneven road surfaces and the dynamic forces of maneuvering. These forces can damage and shorten the useful life of the cab. This isolation has typically been provided by elastomeric cab mount elements placed between the cab and frame. However, these cab mounts do not provide any enhancement in ride quality for the driver or passenger. This requires the cabs to be equipped with expensive ergonomic seats for driver and passenger comfort.
To improve the ride qualities of conventional style trucks, a cab suspension system has evolved which provides additional cab vertical excursion thereby lowering the vertical accelerations felt by the driver, thus improving the comfort level for the driver. This type of suspension system allows the cab to rotate about the front cab mounts and uses relatively soft springs at the rear of the cab to provide an increase in vertical movement of the cab relative to the frame. Although marginally successful this approach has major drawbacks. While providing beneficial vertical movement, to enhance comfort, the system also induces a pitch or fore and aft motion to the driver of similar magnitude. These fore and aft inputs are documented as being detrimental to human comfort (see ISO 2631).
In this type of cab suspension system, the movement of the cab is made difficult by the interface between the hood and cab. As such, design concessions must be made in the mounting of the hood to allow the movement of the mating cab structure. One current design mounts the hood rigidly to the frame at both the front and near the rear of the hood. Cab movement is limited by the clearance between the hood and cab. Large gaps between the hood and cab are required to allow this relative movement. Other design solutions allow the hood mounting to absorb the cab movements but do not provide for any vertical movement of the cab about the front attachment to the chassis.
Another issue with this cab suspension system is the length of the cab on current vehicles. This solution was designed before the advent of the longer integrated sleeper cabs allowed by the change in truck length regulations. Manufacturers use the same solution for both the shorter non-sleeper cab and the sleeper cab, which can be more than twice the length. This means the vertical travel at the driver's position is reduced by approximately 50% affecting the driver comfort.
Current tilt hood designs can be complicated solutions. These designs provide the function of allowing the hood to rotate about a point at the front and near the lower edge of the front face of the hood. The hood is typically mounted somewhere along this axis. Due to frame movements, designs incorporate different features to allow isolation of the hood from these frame movements. Separate components are sometimes included to allow movement of the hood relative to the cab when the two are coupled in the closed position. No current solution provides for a hood suspension system to allow isolation of the hood from road inputs. As such, the hood may be subjected to fatigue inducing vibrations which can reduce the life of the hood.
Cab suspension systems have been suggested that use suspension elements at the four corners of the cab. Springs with low springs rates allow for additional vertical travel of the complete cab. This solution can be used to improve the comfort for the occupants. Unfortunately, this approach also allows for a secondary pitch motion which consequently detracts for any improvement that might have been possible.
Therefore, a need clearly exists for a new design for the cab and hood of a semi-trailer truck that maintains or improves rider comfort while also reducing the problems associated with current cab and hood suspension systems and allowing hood tilt for easy access to the engine. The instant disclosure of a cab and hood suspension system with hood tilt is designed to address at least some aspects of the problems discussed above.